Recording materials for waterless lithographic printing, where a laser-sensitive layer is removed, are already known. Thus, DE-A 25 12 038 describes a material which consists of a substrate, an intermediate layer which contains particles absorbing laser energy (in particular carbon black), nitrocellulose and a crosslinking agent, and a silicone rubber layer. Aluminum, paper and plastic are mentioned as substrates. To prevent the heat generated by the laser from being conducted away by the aluminum, the aluminum surface is preferably provided with an insulating layer of an oleophilic resin. The plate is exposed to infrared or visible laser radiation, preferably from an Nd-YAG laser or an argon laser. In the parts which the radiation strikes, the intermediate layer is oxidized and combusted. Consequently, the silicone layer present on top becomes detached and can be removed with an organic solvent. However, the recording material has only relatively little sensitivity. Moreover, the plates produced therefrom permit only a short print run.
EP-A 573 091 and EP-A 685 333 likewise describe a material for the production of waterless offset printing plates. Once again, it comprises a substrate having an oleophilic surface, a recording layer which is applied thereon, is not more than 3 .mu.m thick and contains a substance which converts radiation into heat, and a cured silicone layer. The substrates used are generally films of polyester, polycarbonate or polystyrene. Polyolefin-coated paper is also suitable. Aluminum substrates are also mentioned; however, these must be provided with a special oleophilic coating. Carbon black and pigments and dyes which absorb in the infrared range are mentioned as substances which convert radiation into heat. The recording layer may also comprise a metal, e.g. bismuth, tin or tellurium, applied by vapour deposition. This metal layer is not more than 25 nm thick. The recording material is provided with an image by means of laser radiation and is then rubbed dry. During this procedure, the irradiated parts of the recording layer are removed together with the silicone layer present on top. Offset printing plates having a polyester substrate permit only relatively short runs in generally small-size, low-speed printing presses. The potential uses of such printing plates are therefore greatly restricted.
EP-A 580 393 discloses, inter alia, a three-layer recording material for the production of waterless offset printing plates. It comprises in general a substrate which reflects IR radiation, for example a substrate of degreased, bright-rolled aluminum or a polyester film, on which a reflecting aluminum layer has been applied by vacuum vapour deposition or by sputtering. An IR-absorbing layer and a silicone top layer are then applied to this substrate. The IR-absorbing layer is removed by imagewise exposure to laser radiation of appropriate wavelength. Consequently, those parts of the silicone layer which are present on top become detached and can be removed mechanically, for example by means of brushing. The metallic or metallized substrate has only little affinity to water. The disadvantage of such a recording material is once again the low adhesion between the substrate and the layer present on top. A printing plate produced therefrom accordingly gives only a short print run.
According to EP-A 644 047, a further layer which itself does not absorb laser radiation but, under the action of laser radiation on the IR-absorbing layer present on top, undergoes thermal decomposition with formation of gaseous products is arranged between the substrate and the IR-absorbing layer. The thickness of this further layer is chosen so that it undergoes only partial decomposition. In general, it is from 1 to 30 .mu.m thick. An adhesion-promoting layer, for example a layer of a silane or a protein, may also be arranged between substrate and thermally decomposable layer.